The Department of Energy’s Office of Environmental Management, responsible for cleaning up radioactive waste from five decades of nuclear weapons production and testing, requested the National Academies to examine requirements for the technology and performance of waste forms in the context of the disposal systems that would contain the waste forms. Among the major messages of the report, the committee found that two characteristics of waste forms govern their performance in disposal systems: (1) capacity for immobilizing radioactive or hazardous constituents and (2) durability. The committee also addressed the legal and regulatory factors that underpin requirements for waste form performance.